The present invention relates generally to fiber optic transducers and, more particularly, to single fiber displacement transducers suitable for detecting linear and rotational movement of a deformable reflective surface.
An example of the state of the technology up to the point of this invention is taught in the J. H. Porter et al U.S. Pat. No. 4,071,753. The fiber optic transducers taught in the Porter patent consist of separate input and output optical fibers. The output fiber is optically positioned relative to the input fiber so that a predetermined portion of the optical power carried by the input fiber is coupled into the output fiber and the modulated optical power received by the output fiber is carried away from the transducer through the output fiber.
Other examples of multi-fiber optic transducers are taught in U.S. Pat. Nos. 3,394,976; 3,789,667; 3,789,674 and 3,961,185. Each of such transducers operate on the same general principle as those taught in the 4,071,753 patent wherein light is introduced through an input fiber and is reflected off of a movable or deformable reflective surface to produce a modulated beam of light which is coupled into an output fiber through which the modulated light is carried away from the transducer to a detector.
The problem with these prior art devices is that they do not provide the requisite sensitivity in detection of displacement of the reflective surface under certain conditions and, since they are multi-fiber arrangements, they are not suited for the production of micro-miniaturized assemblies. Therefore, it has been an object of on-going investigation to develop single fiber optical transducers which would provide enhanced sensitivity for detecting minor deflections or movements of a movable or deformable reflective surface but are readily adaptable to micro-miniaturized constructions.
However, in prior single fiber assemblies, it has been standard to align the fiber axially with its face perpendicular to the axis of the fiber and essentially parallel to the movable or deformable surface. With such assemblies, a cone of light symmetric with the axis of the fiber is projected from the fiber onto the reflective surface and a cone symmetric with the axis is reflected back toward the fiber face where a fraction of the returning light reenters the fiber for transmission back through the fiber. The sensitivity of these assemblies to displacement or deflection of the reflective surface (i.e., the change in the intensity of light reentering the fiber as a function of a change in the distance of the reflective surface from the fiber face as the surface moves) has been found to be acceptable when the initial distance of the fiber face from the reflective surface is relatively short (i.e., up to about 50% of the diameter of a fiber having a numerical aperture of about 0.5). However, at greater distances, the sensitivity to deviation in distance of the reflective surface from the fiber face is not adequate for practical use.
Thus, it is an object of the present invention to provide single fiber optical displacement transducers which have the requisite sensitivity to changes in distance of the reflective surface from the fiber face over a relatively broad range of distances and are amenable to fabrication in micro-miniaturized assemblies.
It is another object of this invention to provide single fiber transducers exhibiting a sensitivity curve such that any small movement of the reflective surface relative to the face of the fiber will result in a significant change in the intensity of reflected light reentering the fiber.
It is a further object of this invention to provide single fiber optical transducers which may be used to sense linear and/or angular displacement caused by changes in pressure, force, torque, acceleration, temperature, electric or magnetic fields applied to a reflective surface.
It is a still further object of this invention to provide single fiber optical transducers which are simple in construction and which may be utilized in a wide variety of potential applications.